Bacterial biofilms are medically important and continue to account for a major percentage of microbial infections in the body. Although vast amounts of knowledge have been obtained in the field of biofilm research, the regulatory mechanisms that determine the development and triggering of biofilm formation are only starting to be elucidated. It has been hypothesized that bacteria might exploit cation concentrations to activate mechanisms required for biofilm formation; however, mechanistic information concerning this process has not been obtained. A genetic screen for mutants in E. coli with altered biofiolm phenotypes indicated that NhaR, a sodium pump regulator, plays an important role in biofilm formation. Moreover, data suggest that NhaR may be involved in the activation of the pgaABCD operon, required for synthesis of a biofilm polysaccharide adhesin. Specific aims include the molecular characterization of the interaction of NhaR with the pgaABCD operon with the long-term goal of beginning to elucidate the physiological significance of NhaR and cation concentration in biofilm formation.